Demand meters are used in the electric utility industry to measure the maximum rate of energy used averaged over a given time. In the past, the devices have been complex, mechanical or thermal devices and have had two primary requirements for displays which wwere that (1) they provide a rugged, reliable display of the quantity measured, and (2) the display be nonvolatile so that the removal of power did not cause loss of the information displayed.
Recently, electronic components have come into use which allow demand meters which offer greater resolution at less cost, however, the display and nonvolatile memory requirements are not well served by conventional purely electronic systems.
Various systems developed in the past to meet the requirements have been complex and costly. Among the various types developed are those position sensors that produce electrical outputs having a magnitude or waveform related to the angular displacement of the movable member such as those shown in the U.S. Pat. No. 3,702,467 granted to Melnyk and U.S. Pat. No. 3,873,916 granted to Sterki. Other tyes of sensors have relied on converting an analog signal corresponding to the position of the movable member and converting it into a digital code representative of the angular position such as the U.S. Pat. No. 3,238,523 granted to Masel, et al. Finally, very complex signal related systems have been used in which the electrical output has a phase angle related to the angular displacement such as those exemplified by U.S. Pat. No. 4,007,454 granted to Cain, et al and U.S. Pat. No. 4,238,782 granted to Ogasawara.
While systems in the past have relied on wedge-type capacitive sensors, relatively complex circuitry was required to provide the proper series of input signals and/or for processing the sensor output signals to provide complex, final output signals.
In the U.S. Pat. No. 3,198,937 granted to Wooster which is a digital to digital converter, reference signals of progressively different phases were generated simultaneously and simultaneously provided to the different electrodes around a shaft whose angular position was to be determined. The sensor output signal was then provided to a phase comparator along with all the reference signals to be compared so a signal could be generated to cause angular rotation of another shaft.
In the U.S. Pat. No. 3,766,544 granted to Batz which is an analog to digital converter, sequential encoded sets of reference signals having two phases are provided to all the different electrodes around a continuously running shaft. The sensor output signals are then compared with the time sequence of the encoded reference signals to provide the angular position at the time the reference signals were provided.
None of the above systems provided a straight forward digital to digital system of sensing the position of the wheels of a cyclometer or the pointers of a dial register.